Bridge wire and method of making same



Dec. 12, 1961 H. J. GODFREY BRIDGE WIRE AND METHOD OF' MAKING SAME 5 Sheets-Sheet 1 Filed Oct. 28, 1955 OOM -only OOw |OOb |oom

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.n n IMMDICKKWAUF Dec. 12, 1961 H. J. Gom-REY BRIDGE MIRE AND METHOD oF MAKING SAME 3 Sheets-Sheet 2 Filed Oct. 28, 1955 Dec. 12, 1961 H. J. Gom-'REYA BRIDGE WIRE AND METHOD 0E MAKING SAME 3 Sheets-Sheet 3 Filed Oct. 28, 1955 It will be seen from the above data that the optimum combination of tensile strength, ductility, and elastic properties of the wire are obtained when the drawn wire is given a heat treatment within theV range of 450 to 800 F. `and more strikingly at temperatures from 450 to 750 F. v

In the prior Ymethod wherein the cold-drawn wire is passed through a molten bath of zinc to coat or galvanize the wire and deposit on it a corrosive resisting coating, it is necessary to maintain the zinc at about 850 F. which is about 60 higher than the melting point and the wire must be kept in the bath a sufficient time to raise the temperature of the wire to permit alloying of the zinc with the surface of the steel Wire core. But subjecting the wire to the molten zinc bath at 850 F. produces a bridge wire which does not have a high tensile strength as the wire would have if the coating were applied to the steel wire by hot dipping at lower temperature, or as high as the iinished lwire would have if given a heatV treatment at a temperature lower than that of molten zinc and otherwise coated without subjecting the wire to such a high temperature.

In a preferred method of practicing myinvention the cold-drawn steel wire is hot dipped in a molten bath con prising a mixture of zinc and tin which may be maintained molten within the range of temperatures which produces optimum combination of tensile strength, ductility and elastic properties and at the same time a corrosive resistant coating of zinc-tin alloy is deposited on the steel wire. Not only does this procedure produce a bridge wire having materially higher tensile strength, better ductility and elastic properties, than the wire produced by the hot dip zinc galvanizing method, but the wire coated with the zinc-tinY alloy has better corrosive resistance.

The lowest practical galvanizing temperature using zinc alone is about 850 F., it having been found that the temperature of the molten bath should be maintained higher than the melting point to insure against freezing of the metal in the bath and to obtain proper coating of the-wire. I have found that by coating the wire in a molten bath containing zinc and tin that the temperature of the molten bath may be maintained within the range of temperatures producing optimum tensile strength and elastic properties and that an immersion time of the order of 30 seconds will produce a corrosive resistant coating which is better than a coating deposited from a molten zinc bath. For example, a molten coating bath made up of 70% zinc and 30% tin may be maintained in the neighborhood of 750 F. (approximately 50 higher than the melting point of an alloy of 70% zinc-30%-tin) and if the wire is immersed in this molten bath for 30 seconds, a zinc-tin alloy coating is deposited on the steel wire which has better corrosive resistance than coated bridge wire produced by the hot dip method wherein the galvanizing coating bath is zinc alone which must be maintained at about 850 F., and at the same time the wire is given a heat treatment which imparts the desired higher tensile and yield strengths to the coated steel Wire.

The data in Table l shows that heating the wire at a temperature of 750 F. instead of 850 F. increases the 'tensile strength of the wire 7000 p.s.i. and the yield strength for .2% Set by 22,000 p.s.i. and the elongation is more than 4% in l0 inches.

I have conducted tests to Vcompare the strengths of steel wire which was produced by the method of hot dipping in molten zinc and hot dipping in a molten alloy of zinc and tin; in this instance the alloy being 72% zinc and 28% tin. In these tests, samples of wire were made from ten diierent heats of steel. The diierent samples were drawn from rod in the usual way and the cold-drawn wire was then coated with a corrosive resistant coating, so that the finished bridge wire was processed to have a diameter of about .196 inch (including the coating). The average tensile strength of the samples made from the heats and coated by dipping in a molten bath of pure zinc was 228,000 p.s.i.; whereas the average tensile strength ofthe samples from the same heats and coated by immersion in a molten bath of 72% zinc and 28% tin was 244,000 p.s.i., showing an improvement in tensile strength of 16,000 p.s.i. The stress for 0.2% Set was 187,000 and 213,700 p.s.i. respectively, or an improvement of 26,700 p.s.i. In comparing the tensile strengths of these samples with those shown in Table I, it should be noted that the wires reported in Table I were not coated with any corrosive resistant coating. The higher tensile strengths of the uncoated wire (for the same temperature treatment) is due in part to the thickness of coating which is included in theV area of the nished Wire but the coating does not contribute to the strength. Some of the difference may be accounted for by the fact that the tensile strengths given in Table I are from samples all taken from a single coil of wire, whereas the tensile strength given for the zinc-tin alloy coated wires is an average for ten diierent heats of steel. It is common for heats of steel having the same nominal analysis to vary somewhat in tensile strength after processing.

The relative amounts of tin and zinc in the coating bath may varyover a considerable range. As the percentage amount of tin is increased, the melting point of the alloy is decreased. Also, as the percentage amount of tin is increased, the temperature at which the coating bath can be maintained molten is decreased Vand the thickness of the corrosive resistant coating deposited on the steel wire is decreased.

In FIG. 3 there is shown graphically the results of test to compare the thickness of coating with varying tin content ot the coating bath made up of zinc and tin. This graph show the eect of tin content on the thickness of zinc-tin alloy coatings.

In each case the finished coated wire is 0.196 inch, including the steel wire core and the alloy coating. It will be seen that as the tin content is increased the thickness of the coating is decreased. Thus, for example, as shown in FIG. 3, coated bridge wire .196" diameter which has a coating applied from a molten bath containing zinc and 10% tin, would have a net steel wire core diameter of .192+ and a coating thickness of about .002" and one which has a coating applied from a bath containing 70% zinc and 30% tin would have a net steel wire core diameter of .193+ and a coating thickness of about .0015". FIG. 3 also shows that a bath containing 10% zinc and 90% tin would produce a coating thickness of about .0005". Also, it may be mentioned here that the temperature of the molten bath may be decreased as the percentage amount of tin is'increased.

There is shown in FIG. 4 the zinc-tin Constitutional Diagram, wherein the melting points for zinc-tin m'uitures are shown. And it should be borne in mind also that in practice the molten bath preferably should be maintained about 50 higher than the melting point to guard against freezing of the coating bath during actual plant operations. This graph also shows the preferred operating temperature for the bath for varying tin content; see curve labeled Temperature of Bath.

FIGS. 6 and 7 are photomicrographs which show that the coating applied from a molten bath of zinc differs appreciably from the coating applied from a molten bath of zinc-tin alloy. FIG. 6 is a photomicrograph (500 X) of a bridge wire, .1955 diameter, made by the known hot dip method wherein the steel wire is passed through a molten bath of zinc maintained at 850 F. with an immersion time of 30 seconds. The steel wire core portion at the bottom is designated S1; the thin layer next to the steel is the zinc-iron alloy, designated Z-I, and the top layer is the zinc layer, designated Z. It should be noted that the zinc-iron alloy layer Z-I is almost 50% of the thickness of the coating. FIG. 7 is a photomicrograph (500 X) of'a bridge wire, .196 diameter, made according to the process ofthe invention wherein the steel wire is passed through a molten bath of 70% zinc and 30% tin maintained at a temperature of 750 F. with an immersion time of 30 seconds. The steel wire core portion at the bottom of the photomicrograph is designated S2; the thin layer next to ythe steel is the zinc-tiniron alloy layer and is designated Z-T--I and the top layer is zinc-tin alloy, designated Z-T. It should be observed that the thin zinc-tin-iron alloy layer, Z-T--L is only about of the thickness of the coating. inasmuch as the iron alloy layers tend to be brittle, the thinner iron alloy layer in the bridge wire, as shown in FIG. 7, is advantageous in that it permits the Wire to bend to a smaller radius without cracking ofi or aking of the coating. To avoid confusion in terminology, it will be understood that in describing the iinished bridge wire, the steel wire portion in the center of the bridge wire will be referred to as the steel wire core portion which is surrounded by the coating comprising an ironalloy layer, which in turn is surrounded by a layer of the coating metal, viz.-zinc, if zinc alone is used, zinc-tin alloy if a mixture of zinc and tin is used. It will be understood that the photomicrographs are taken at the periphery of a cross-section of the wire at right angles to its longitudinal axis.

In addition to the advantages mentioned above, my improved bridge wire may be wrapped on a smaller diameter mandrel than bridge wire heretofore available and made by the hot dip process `wherein the wire is coated by hot dipping in molten Zinc. I have found, for example, that my improved bridge wire made by coating the steel wire with tin-70% zinc alloy can be wrapped on its own diameter without cracking, spalling, or aking of the alloy coating. In contrast to this, when hot galvanized bridge wire heretofore commercially available was wrapped on its own diameter it was found that the coating cracked, spalled or aked. The presently accepted specifications for bridge wire usually require that the wire be capable of being wrapped on a mandrel live times its diameter without cracking or flaking of the zinc coating. it will be readily seen that my improved bridge wire will meet a more stringent specification than present specifications, namely that the bridge wire be capable or being wrapped on a mandrel two times the diameter of the wire without cracking or iiaking. Furthermore, it will meet more stringent specications with respect to strength.

It is not practical to increase the tin content of the zinc-tin coating mixture over 50% ecause the coating of such higher tin content 'becomes too thin to form an adequate protection against corrosion. referably the zinc-tin coating alloy should contain about 30% tin, as this produces a very good corrosive resistant coating and permits of maintaining the temperature of the molten bath in which the steel wire is dipped at a temperature no higher than 750 F.; this being within the range of temperature for producing the desired higher tensile strength; bearing in mind that optimum combination of desired properties is produced when the wire is given a heat treatment at a temperature within the range 450-750 F.

In order to obtain the highest tensile strength it is desirable not only to coat at temperatures below 750 F., but also the wire should be immersed only for a short time. The effect of time and temperature of immersion on tensile strength of cold-drawn .196" diameter bridge Wire is shown graphically in FIG. l. For hot dip coatings, suticient time of immersion must be allowed to raise the temperature of the wire to permit alloying of the coating with the surface of the steel wire core. A practical time is 30 seconds but in practicing my process it is not practical to reduce the time below 5 seconds. It will be seen from the graph of FIG. l that a time of immersion may be selected within the range of 5 to 30 seconds. in some instances even a longer time of immersion may be employed but it should not be so long as to materially impair the tensile strength.

The eiect of time and temperature on the elongation of the steel wire is shown in FIG. 2. Elongation is usually a part of the specication for bridge Wire and it is sometimes required that it exceed 4% in a l0 inch length. However, the wire does not stretch permanently unless the yield stress is exceeded and in practice it is usually considered satisfactory for service if the percentage elongation of the finished bridge wire exceeds the percentage elongation of the cold-drawn wire.

It is important that the coating aord protection against corrosion because failure of bridge wire in service is most frequently attributed to penetration of the protective coating which permits corrosion of the underlying steel wire core. Bridge wire made according to my invention has a resistance to corrosion at least equal to that of the hot galvanized bridge wire now commercially available. And by practice of my invention according to my preferred method, a bridge wire may be produced which has a coating which affords better resistance to corrosion. I have.

made salt spray tests on hot galvanized bridge wire in which the coating was zinc and comparative tests on bridge wire made according to my invention in which the bridge wire was coated with a zinc-tin alloy by hot dipping the steel wire in a molten bath of zinc-30% tin. The samples of bridge wire coated by hot dipping in molten zinc started to rust in these tests after 250 to 450 hours. The samples of 30% tin-70% zinc alloy coated bridge wire did not start to rust under similar conditions until 400 to i000 hours.

Although I prefer the hot dip method for producing my improved bridge wire, in which the cold-drawn wire is hot dipped at a temperature not exceeding 750 F., because it has been found that improved tensile, yield and elastic properties may be obtained at this temperature and at the same time a more edective corrosion resistant coating may be applied at the same time, nevertheless it may in some cases be desirable to take advantage of the improved tensile and elastic properties which may be produced by heat treating the `cold-drawn steel wire at temperature considerably lower than 750 F. or lower than are practical with a coating bath of molten zinc-tin alloys. In such instances, the steel wire may be heat treated at the lowest temperature within the range of 450"V F. to 750 F. which produces the highest tensile and yield strengths and then provided with an adequate protection against corrosion by an electrogalvanizing step which may be carried out at ambient atmospheric temperature or somewhat higher but not at such a high temperature as to adversely a ect the improved tensile and yield strength imparted by the heat treatment. Or, if desired, the colddrawn steel wire may be electrogalvanized and then heat treated at a temperature above 450 F. but not so much higher as would adversely aiect the electrodeposited protective zinc coating or adversely aiect the tensile strength unduly. An iilustrative example of the electroplating method is set forth later on.

Another property of bridge wire which is of practical importance is the free coil diameter. This may be deined as the natural diameter of a single coil of the wire. The free coil diameter of bridge wire must be large enough so that when the wire is being strung in single strands to its position at the bridge site there will be no undue curl or waviness. `It has been found in practice that a free coil diameter of 6 to 7 feet or larger is satisfactory.

The free coil diameter of wire is increased by the heat treatment employed to obtain the desired physical properties. Experiments were made to show the effect of the heat treatment on free coil diameter.` The results are shown graphically in FIG. 5.

The usual free coil diameter of the wire as drawn is about 21/2 feet. It will be seen that at 850 F. (the usual temperature heretofore employed for hot galvanizing) the free coil diameter of as drawn wire .196 diameter is increased to about 13 feet as indicated by curve B1. At 750 F. (the temperature employed in my preferred method of producing bridge wire having a zinc-tin corrosive resistant coating) the free coil diameter of as drawn wire .196 diameter is increased to about 9 feet (see curve B1) which is a satisfactory free coil diameter for Stringing the bridge Wire strands at the bridge site.

lf the heat treatment given the wire is at a temperature too low to produce a sufficiently large free coil diameter, the desired larger free coil diameter of the iinished bridge wire may be produced by adjusting the angle of the final die in wire drawing in relation to the axis of the Wire, or by a mechanical .straightening operation, provided it is done prior to the heat treatment. Curve B2 (FIG. 5) shows the effect of heat treatment on .196 diameter Wire which has been Wire drawn to n larger free coil diameter. As shown in curve B2, if the free coil diameter of the as drawn Wire is increased to 5 feet, the free coil diameter after heat treatment at 750 F. is increased to about 14 Y I feet. This is approximately the same as the free coil diameter of Wire given a heat treatment of 850 F. (the temperature for hot dipping in molten zinc) but which had a free coil diameter of 21/2 feet as drawn (see curve B1), Another way to enlarge the free coil diameter prior to heat treatment is to subject the Wire to a mechanical straightening operation providing this is done prior to the heat treatment which will further increase the free coil diameter in a manner similar to that shown in FIG. 5. One device for subjecting the wire to a mechanical straightening is the so-called barrel straightener, in which the wire is passedV through a rotating tube containing offset guides. A simpler device which may be empioyed for straightening the wire is diagrammatically illustrated in HG. 8. This device comprises a pair of large pulleys and 11 mounted in tandem for rotation on their respective axes, each having a concave face around which the wire Wis wrapped, once around, as shown in the drawing. The Wire is pulled in the direction of the arrow. Between the two pulleys 10 and 11 is mounted a bracket 13, having a slot Vit, in which is mounted and clam-pcd a shaft 15, on which is rotatably' mounted a small roller 16. The roller bears downwardly on the wire W between the pulleys 10, 11 and the pressure on the `wire may be adjusted by adjusting the shaft 15 upwardly or downwardly in the slot 14. Free coil diameter is controlled by adjusting the pressure of the roller 16 on the wire. This straightening should -be done before the heat treatment, otherwise the elastic properties may be impaired.

Referring now to FIG. 9 wherein is diagrammatically illustrated one form of apparatus or system for coating bridge wire by a hot dip method according to the invention, cold-drawn Wire W, which has been cold drawn from 0.8% carbon steel rod in the usual way to the desired diameter, is placed on a reel 20. lt will be understood that the cold-drawn wire will have been drawnto a diameter, which then ultimately coated with the corrosive resistant coating will have a predetermined desired or speciied diameter; for example, .196". The reel 20 is mounted for rotation and serves as a pay-off reel. The wire W is passed through a bath of lead Z1 maintained in molten state at a temperature of 650 F.-725 F. in a tank 22 mounted in a suitable furnace arrangement 23 to supply the necessary heat to maintain the lead molten and at the desired temperature. Suitably mounted sinkers 24, 25 cause the wire to pass under the surface of the molten lead.

VThe purpose of the molten lead is to burn olf any soap or the like picked up by the Wire in the drawing operation and otherwise to assist in cleaning the surface of the wire. This is not a heat treatment as such because the controlling heat treatment in this system is given the Wire in Y.the coating bath of molten zinc-tin alloy after the wire has been cleaned.

After immersion in the molten lead 21 the wire, now designated W2, is cooled by water sprays 26. It yis then passed through a bath of aqueous hydrochloric acid 27, preferably a 15% solution, maintained in tank Z8 and preferably at a temperature of about 140 F., to clean the surface of the wire of oxides or other contaminants. Snitably mounted, sinkers 29, guide the wire under the surfaces of the hydrochloric acid Z7. The wire, now

designated W3, is given a water Wash to remove excess or adhering acid by means of water4 sprays 31. The wire is then passed over a suitableY guide pulley 32, into and through a ilux 33 comprising a zinc ammonium chloride solution maintained in tank 34 at a temperature of about 130 F. A suitably mounted sinker 35 guides the Wire through the iiux solution. The wire, now designated W4, is passed over guide pulleys, l36, 37, thence through a coating alloy 33 of zinc-tin, in tank 39 mounted in a furnace dit; the furnace serving to maintain the alloy molten and at desired temperature for the heat treatment and for coating the wire. i prefer to use a coating alloy of 70% zinc and 30% tin and to maintain the temperature of the molten bath 3S at a temperature of 750 F., and to adjust the speed of travel of the Wire to provide an immersion time of 30 seconds in the molten bath. The wire -is caused to pass under the surface of the bath by a suitably mounted, rotatable pulley 41. As the wire, now designated W5, passes from the heat treating and coating bath of zinc-tin alloy 3-8 it is wiped by a wiper 42, containing a mixture of charcoal and oil, mounted above the surface of the bath. The hot wire W5 is cooled by water sprays 43 and 43 to insure solidiiication of the coating alloy, and passes over water cooled pulley 44, thence over pulleys 4S', 46 to a winding reel mounted on a take-up block, as coated and iinished bridge wire.

The cooling of the zinc-tin alloy coated Wire after it leaves the coating pan 39 is an important step of the process. Because of the nature of the alloy the zinc portion begins to solidify first, leaving the liquid part of the alloy richer in tin. As the cooling proceeds the zinc tends to solidify as pure zinc until at a temperature of 390 F. the melt containing approximately 91% tin and 9% Zinc solidities as a eutectic. The iinal solidification temperature is 360 F. below the operating temperature whereas for conventional hot galvanizing with zinc the solidication temperature is only approximately 60 F. below the operating temperature. The methods of cooling conventional galvanized wire are not sufficient to properly solidify the zinc-tin alloy coating prior to running the wire over guide sheaves following the coating pan. Additional Water sprays (43),V at or prior to the rst guide sheave followed by a second Water spray v(43') after the iirst guide sheave are used to effect proper cooling and prevent the zinc-tin alloy coating from being roughened or scraped.

Although in practicing my process I prefer the conditions as set forth immediately above it will be understood from the preceding discussion of my invention that the amount of tin in the zinc-tin alloy may be varied and the temperature of the molten alloy may be varied. The amount of tin in the alloy should however, not be increased to the point where the coating deposited on the wire is too thin for adequate corrosive resistance, nor should it be decreased to a point where it requires a temperature so high that the benefits of lower heat treatment temperature are lost. That is to say, the tin content in the zinc-tin alloy should not appreciably exceed 50% and it should not be appreciably less than 10%. lAlso, the'time of immersion in the molten bath should be enough to insure sufiicient heating of the wire to effect the heat treatment and to insure proper alloying of the coating alloy with the iron at the surface of the steel core of the Wire. lIhave found that thirty seconds is a suitable time. It is impractical to reduce the immersion time lower than tive seconds.

In FIG. 10 there is diagrammatically illustrated a different form of apparatus or system for employing important features of my invention. In this system the colddrawn wire may be given a heat treatment at a temperature lower than that when the corrosive resistant coating is applied by hot dipping in a bath of zinc-tin alloy. In this system the cold-drawn Wire, drawn to desired diameter to produce a predetermined diameter after the coating is applied, is given a heat treatment for the desired time by passing it through a suitable heat treating bath which may be maintained at a temperature above 450 F. but lower than 750 F., and the wire is then coated 4by an electrolytic method.

A fused mixture of sodium and potassium nitrate may be used for the temperature range 450 F. to 750 F. Altematively molten lead may be used for the temperature range 65.1 F. to 750 F. Heating in air may also he used although this method is somewhat more dilicult to control. When an electrolytic method of coating is used the coating metal is deposited directly on to the steel wire core without the formation of an intermediate alloy layer such as is formed by the hot dip method of coating.

in the system illustrated in FIG. 10, the cold-drawn wire W is unwound from a pay-ofi reel 120, and is passed through a bath `60 of molten lead which may be maintained at any desired temperature in the range of 650 F. -to 750 F., preferably near 650 F. The tank 61 holding the lead is maintained :in a furnace 62- to supply the necessary heat. The wire is guided by suitably mounted guide pulleys 63, 66 and sinkers 54, 65. The wire, now designated Wa, is cooled by water sprays 67, and passed through a bath 68 of hydrochloric acid solution, preferably a 15% solution which is preferably maintained at a temperature of about 100 F. in the tank 69. Guide pulleys 70, 73 and sinkers 71, 72, guide the wire so that it passes through the acid solution, to clean the wire. The wire, now designated Wb, is given a water wash to remove adhering acid by means of water sprays 74. The wire is further cleaned by passing it through an electrolytic bath 75 comprising a solution ot nitric acid, preferably, at about 8% concentration, in tank 80. A current, from a 6 v., D.C. source, is passed through the bath, the positive side 76 being connected to the wire providing an anode, and the negative side 77, provided with a variable resistance 78, beingrconnected to a cathode 79. The wire is guided through the bath by pulleys 31, 83 and sinker 82. The wire, now designated Wc, is given a water wash in tank 85 and then guided by pulleys 86, 88 and sinlter 87 through an electrolytic bath 90 in tank 91. This bath 91 comprises a solution of sulphuric acid, preferably about 40% concentration. A current from a 6 v., D.C. source, is connected on its positive side 92 to the Wire, thus providing an anode and the negative side 93, provided with a variable resistance 94, is connected to a cathode 95. The wire, now designated Wd, is now properly cleaned and is ready to be electroplated to provide the wire with a corrosive resistant coating. In the system illustrated, the wire Wd is passed through a zinc plating bath 96 in tank 97 guided by pulleys 9S, 102, and sinkers 99, 101.

The wire is connected to the negative side 103 of a source of 6 v., D.C. current. The positive side 104, provided with a variable resistance S, is connected to zinc anodes 106. Wire 103 is in turn connected to contacts 100 and wire Wd travels through the electrolyte solution 96 in engagement with contacts 100. Thus, a zinc, corrosive resistant coating of desired thickness is deposited on the steel wire core. The finished bridge wire, now designated We, pulled through the system by means of pull rolls 107, 08, is wound on a reel 109 mounted in take-up block 110.

The system employing electroplating of the corrosive resistant coating on the steel wire core, as distinguished from the hot-dip method, has the advantage of providing a lower heat treating temperature and therefore obtaining correspondingly higher tensile strength in the finished wire. Furthermore, the wire may be heated at temperatures lower than are practical with zinc-tin alloys and at the same time adequate protection against corroSion may be obtained. The electrolytic method of coating may be carried out at ambient atmospheric temperature or a little above, and the heat-treating operation to produce good tensile strength and elastic properties may be carried out before or after galvanizing, although it is preferable to heat-treat before galvanizing.

As one example of the electroplating method, some Tensile strength p.s.i 245,000 Total elongation in 10 percent 5.9 Reduction of area do- 36 Proportional limit p.s.i 130,000 0.7% elongation p.s.i 184,000 0.1% Set p.s.i 203,000 0.2% Set p.s.i 213,000

These properties are considerably higher than the propertics of regular galvanized bridge wire made by the hot dip method of coating wherein the coating is applied by hot dipping in a bath or" molten zinc.

In the foregoing description the steel rod stock which is reduced to bridge wire dimension by cold drawing has been referred to as high carbon steel rod. This is the terminology which is used in the trade to designate the kind of steel used for bridge wire; standard textbooks on the subject giving a more detailed specification as follows: C, 0.70 to 0.85%; Mn, 0.50 to 0.75%; Si, 0.15 to 0.35%; P, under 0.04%; S, under 0.04%; balance iron and incidental impurities. See The Making, Shaping and Treating of Steel, fifth ed., copyright 1940, Carnegieillinois Steel Corporation. t will be understood, however, that the content of carbon in the rod stock for bridge wire may vary within limits and may be as low as 0.7 or as high as 0.9%. The preferred analysis for bridge wire cables is about 0.8% carbon.

lty will be seen from the foregoing disclosure and description that my invention provides a method whereby bridge wire may be produced, having an average tensile strength of 240,000 p.s.i. or greater; an average stress for 0.2% permanent set of 200.000 p.s.i., or greater; a corrosive resistant coating of zinc, or zinc-tin alloy for protection against corrosion; a free coil diameter of 6 feet, or larger; a steel core portion containing 0.7% or more carbon; and a bridge Wire which may be Wrapped on a mandrel only twice its diameter without cracking or aking of the coating.

The terms and expressions which I have employed herein are used as terms of description and not of limitation, and l have no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but recognize that various modications are possible within the scope of the invention claimed.

What is claimed is:

1. A bridge Wire having a diameter within the range of 0.150" to 0.250" which comprises a steel Wire core portion made from heat treated cold drawn patented high carbon steel rod stock having the following analysis: C, 0.70 to 0.85%; Mu, 0.50 to 0.75%; Si, 0.15 to 0.35%; P, under 0.04%; S, under 0.04%; and balance iron and incidental impurities, and a corrosive resistant coating surrounding said core portion, said coating comprising an outside metallic layer of metal selected from the class consisting of zinc and zinc-tin alloy having a thickness within the range of .0005" to .002" and bonded to said steel wire core portion, said coated bridge wire having a tensile strength of at least 240,000 p.s.i., a stress for 0.2% permanent set of at least 200,000 p.s.i., a total elongation in excess of 4% in 10 inches, a free coil diameter greater than 6 feet and further characterized by its ability to be wrapped on a mandrel having a diameter no greater than twice the diameter of the wire without cracking or flaking of said corrosive resistant coating and having a corrosion resistance sucient to prevent rusting of the steel core I for over 400 hours when subjected to a salt spray corrosion test.

2. A bridge wirerhaving a diameter between .150 and .250" which comprises a core of heat treated steel wire cold-drawn from patented high carbon steel wire stock the analysis of which is: C, 0.70 to 0.85%; Mn, 0.50 to 0.75%; Si. 0.15 to 0.35%; E, under 0.04%; S, under 0.04%; the balance iron and incidental impurities, said steel core being coated with a corrosive resistant coating having a thickness within the range of .0005 and .002" said coating comprising an outside layer of zinc-tin alloy and a layer of an alloy of zinc, tin and iron lying between said outside zinc-tin layer and said steel core and bonding said coating to said steel core, said coated bridge wire having a tensile strength of at least 240,000 p.s.i., a stress for 0.2% permanent set of at least 200,000 psi., a total elongation in excess of 4% in 10 inches and further characterized by its ability to be wrapped on a mandrel having a diameter no greater than twice the diameter of said Abridge wire without cracking or tlaking of said coating.

3. A bridge wire having a diameter Within the range of .150" and .250" which comprises a steel core of heat treated cold-drawn steel wire, cold-drawn from patented high carbon steel wire stock having the following analysis: C. 0.70 to 0.85%; Mn, 0.50 to 0.75%; Si, 0.15 to 0.35%; P, under 0.04%; S, under 0.04%; the balance iron and incidental impurities; said steel core being covered with a hot-dipped zinc-tin alloy corrosive resistant coating comprising to 50% tin and 50% to 90% zinc, said coating having a thickness within the range of .001" and .002 and consisting of an outside layer of zinctin alloy and a layer of zinc-tin-iron alloy lying between said outside layer and said steel core and bonded to said steel core, said bridge Wire having a tensile strength of at least 240,000 p.s.i., a stress for 0.2% permanent set of at least 200,000 p.s.i and -a total elongation in excess of 4% in 10 inches and having a free coil diameter of at least 6 feet, and having `a corrosion resistance sufficient to prevent rusting of said steel core for over 400 hours when subjected to a salt spray corrosion test, and further characterized by its ability to be wrapped on a mandrei having a diameter no greater than twice the diameter of said bridge wire without cracking or halting of said coating.

4. A bridge wire according to claim 3 wherein the steel core has a diameter within the range of .190 and .200 and the corrosion resistant coating is an alloy comprising about 30% tin and about 70% zinc.

5. A method of producing bridge Wire coated with a corrosion-resistant coating having a corrosion resistance suiiicient to prevent rusting of said wire for over 400 hours in a salt spray test and which has a tensile strength of `at yleast 240,000 psi., a stress at 0.2% permanent set of at least 200,000 psi., a total elongation in 10 inches of at least 4.0%, and having a free coil diameter of at least 6 feet and characterized by its ability to be wrapped on a mandrel having a diameter no greater than twice the diameter of the Wire without cracking or aking of said corrosion-resistant coating, which method comprises heat treating steel wire stock consisting of 0.70 to 0.85% carbon, 0.50 to 0.75% manganese. 0.15 to 0.35% silicon, a maximum of 0.04% phosphorus, a maximum of 0.04% sulfur, and the balance iron and incidental impurities, to form heat treated patented rod; cold drawing the heat treated patented rod and drawing it sufficiently to reduce its diameter to within the range of .150" and .250 and thereby increasing its strength and thereby forming a cold drawn high strength steel wire core, subjecting the cold drawn steel wire core to a cleaning treatment to remove suriace contaminants, iiuxing the surface of the Wire core and passing the clean steel wire core through a molten bath comprising 10% to 50% tin and 50% to zinc maintained at a temperature between 650 F. and 800 F. with an immersion time sufficient to heat treat said steel core to produce a bridge wire having a tensile strength of at least 240,000 p.s.i. and a yield strength sufficient to require a stress of at least 200,000 p.s.i at 0.2% permanent set and to produce a total elongation of at least 4.0% in a 10y gauge length while simultaneously coating said wire with a corrosion resistant hotdipped coating of zinc-tin alloy, the total thickness of which is within the range of .001 to .002.

6. A method according to claim 5 in which the zinctin molten bath comprises about 30% Vtin and about 70% zinc maintained 'at a temperature Vabout 750 F.

7. A method according to claim 6 in which the patented rod is cold drawn to a diameter within the range of .190l and .200" prior to the cleaning step.

References Cited in the file of. this patent UNITED STATES PATENTS 94,935 Barden Sept. 21, 1869 1,552,040 Fowie Sept. 1, 1925 1,567,625 Smith Dec. 29, 1925 1,948,505 Bray Feb. 27, 1934 2,069,658 Renkin Feb. 2, 1937 2,192,901 Elder Mar. l2, 1940 2,283,868 Fowle May 19, 1942 2,482,978 Ilacqua Sept. 27, 1949 2,511,274 Kramer June 13, 1950 OTHER REFERENCES Galvanizing, by Babiik, pub. 1950, E & FF N Sport Ltd., 22 Henrietta St., London WC 2 (pp. 224-226, 250, 357-364).

Making, Shaping and Treating of Steel, pub. 1951, 6th Ed., U.S. Steel Co., pp. 1096, 1117, 1118, 1234. 

